Refrigeration system provided with compressor unloading mechanism



March 27, 1956 R. s. BRECK REFRIGERATION SYSTEM PROVIDED WITH COMPRESSOR UNLOADING MECHANISM 2 Sheets-Sheet 1 Filed Sept. 30, 1952 INVENTOR.

March 27, 1956 R. s. BRECK 2,739,450

REFRIGERATION SYSTEM PROVIDED WITH COMPRESSOR UNLOADING MECHANISM Filed Sept. 30, 1952 2 Sheets-Sheet 2 mm H m r z 8 &

FIG 3 IN VEN TOR.

REFRIGERATION SYSTEM PROVIDED WITH IGWRESSOR UNLOADING MECHANISM Roger S. Breclr, Syracuse, N. Y., assignor to Carrier Corporation, Syracuse, N. Y., a corporation of Delaware Application September 30, 1952, Serial No. 312,272

7 Claims. (Cl. 62-3) This invention relates to a refrigeration system and more particularly to a refrigeration system provided with unloading mechanism for the compressor.

The chief object of the present invention is to provide a refrigeration system including unloading mechanism for the compressor which permits the compressor to remain in operation without doing work.

An object of the invention is to provide unloading mechanism for a reciprocating compressor driven by an internal combustion engine which permits the cylinders of the compressor to be unloaded while the compressor remains in operation driven by the engine thus rendering the refrigeration system of particular advantage when applied to cool storage compartments of vehicles such as trucks and trailers.

A further object is to provide unloading mechanism for the reciprocating compressor of a refrigeration system, the unloading mechanism being responsive to pressure in the liquid line of the system to load or to unload the compressor. Other objects of my invention will be readily perceived from the following description.

This invention relates to a refrigeration system which comprises in combination a compressor, a condenser connected to the compressor, an evaporator placed in a compartment to be cooled, a line connecting the condenser and the evaporator, expansion means in said line, a suction line connecting the evaporator and the compressor and means for unloading the compressor while continuing operation of the compressor, said means being responsive to pressure in the first line.

This invention further relates to a method of operation of a refrigeration system in which the steps consist in compressing gaseous refrigerant, condensing the compressed refrigerant, evaporating the condensed refrigerant, returning the evaporated refrigerant to the compressor, applying a predetermined oil pressure to power elements to load the compressor cylindersand varying the oil pressure applied to the power elements in response to a predetermined change in pressure in the liquid line to unload the compressor.

The attached drawings illustrate a preferred embodiment of my invention, in which Figure 1 is a diagrammatic view of a refrigeration system including the present invention;

Figure 2 is a view partly in section and partly in elevation of a reciprocating compressor provided with the present invention; and

Figure 3 is a sectional view of unloading mechanism for a compressor cylinder.

Referring to the drawings, there is shown in Figure 1 a refrigeration system provided with the present inven tion. The refrigeration system includes a compressor 2 connected by discharge line 3 to an air cooled condenser 4. It will be understood, if desired, condenser 4 may be water cooled. Condenser 4 is connected to a receiver 5, receiver 5 being connected to an evaporator 6 by liquid line 7. An expansion valve 8 is placed in line 7 and serves to meter refrigerant supplied to evaporator 6.

States Patent 2,739,450 Patented Mar. 27, 1956 2 Expansion valve 8, as iscustomary practice, is actuated by means of a bulb 9] placed in contact with suction line 10 of the system. Suction line 10, of course, connects evaporator 6 with the suction manifold (not shown) of compressor 2.

In expansion valve 8 a small opening is drilled across the seat to permit communication with liquid line when unloading is desired. This is necessary owing to the characteristic operation of an expansion valve. A similar result may be achieved by using a capillary by-pass as shown at around the valve.

Evaporator 6 may be placed in a casing 11 disposed in a compartment 12 to be cooled. Compartment 12 may be the storage compartment of a vehicle such as a truck or trailer. Preferably, fan 13 is placed in casing 11, fan 13 serving to draw air from the compartment into the casing and to pass the air through evaporator 6 in heat exchange relation with refrigerant therein to cool the air.

-,A solenoid valve 14 is placed in liquid line 7 between receiver 5 and expansion valve 8. Solenoid valve 14 is controlled by a thermostat 15 responsive to the temperature incor'npartment. i2v as indicated by bulb 16. Predetermined change in temperature in compartment 12 actuates a switch (not shown) in thermostat 15 to open or to close contacts to energize an electrical circuit to move solenoid valve 14 to open or closed positions.

In Figure 2 there is shwn compressor 2 provided with unloading mechanism 20, preferably foreach cylinder of the compressor. A pump 21 is provided for compressor lubrication of moving parts of the compressor. The power elements 22 ofunloading mechanism 20 are connected to pump 23 by lines 23. A relief valve 24 is placed in line 23 to maintain a constant oil pressure to the moving partsof the compressor and to power elements 22. A line, 25is connected to line 23 between the power elements 22 and relief valve 24 and permits oil to be drained from line 23 to the sump 26 of the compressor. A regulating valve 27 is placed in line 25'.

Regulating valve 27 includes. a housing 28, a spring loaded diaphragm 29 which moves valve member 30 to open or to close port 31. Atmospheric pressure and spring pressure are applied against one side of diaphragm 29. A line 32 connects the chamber on the opposite side of the diaphragm to. liquid line 7 at a point between solenoid valve 14 and expansionvalve it. Thus, pressure existing in liquid line 7 is applied against the opposite side of diaphragm 29 urging valve member 36 to close port 31.

The unloading mechanism 20 is best shown in Figure 3.

Unloading mechanism 2t of course,'serves to place the suction valve of a compressor cylinder in inoperative position. Similar mechanism is provided preferably for each cylinder of the compressor when the refrigeration system is employed'for cooling the storage compartment of a vehicle such as a truck or trailer. Mechanism 2% employed to place suction valve 35 in inoperative position includes lifter sleeve 36, lifter pins 37, loading springs 38 and a retainer ring 39. Preferably, such mechanism comprises a self-contained sub-assembly with a removable cylinder sleeve 40 in which the compressor piston 41 operates. Suction gas from the manifold (not shown) enters the suction valve port 42 and passes through such port into the interior of the compressor cylinder when valve 35 is moved awayfrom port 42. When pins 37 in the position illustrated in Figure 3, the suction valve 35 closes at the end of each suction stroke under the urging of suction valve springs 43. After compression the gas in the cylinder, the gas is discharged through discharge valve 44 into the cylinder head space 45 Iins 37 remain retracted while full oil pressure is applied to power element 22 and are moved upward tohold valve 35 in inoperative position when oil pressure on elements through the condenser.

22 is discontinued, as hereinafter described. Power element 22 consists of a casing 46 having a base 47 and a top cover 48. A piston 49 is placed in casing 46 and is connected by a rod 50 to a forked lever Sloperating on a fulcrum 52, placed at one end of cover 48. Lever 51 terminates in portions 53 adapted to engage the lifter sleeve 36 surrounding the cylinder. applies a predetermined pressure to piston 49. In the absence of oil pressure supplied to element 22, piston 49 rests against the bottom cover or base 47. A vent 55 may be provided in power element 22 to permit oil which seeps past piston 49 to return to the crank case of the compressor. If desired, power elements 22 may be placed in the suction manifold of the compressor adjacent the cylinder to be unloaded.

When oil pressure is supplied to power element 22, piston 49 moves upward permitting lever 51 to be urged downward by springs 38 until such movement is halted by sleeve 36 contacting ring 39. Downward movement of sleeve 36 carries pins 37 therewith, thus permitting suction valve 35 to be placed in operative position. When pressure is removed frompower element 22 as by, for example, discontinuing the passage of oil thereto through line 23, piston 49 is forced downward by spring 54-, pivoting lever 51 about fulcrum 52 and urging sleeve 36 in an upward direction to raise pins 37,

thus holding valve 35 away from port 42 with the suction valve held in an open position. No compression of gas takes place in the cylinder and the capacity of the cylinder is zero.

Considering the operation of the refrigeration system, compressor 2 compresses gaseous refrigerant it receives from evaporator 6. The compressed gaseous refrigerant flows through line 3 to condenser 4 where it is condensed by being placed in heat exchange relation with air passed Liquid refrigerant flows from condenser 4 to receiver 5. Liquid refrigerant flows through liquid line 7 to evaporator 6 when solenoid valve 14 is in an open position. Expansion valve 8 regulates the flow of refrigerant to evaporator 6. In evaporator 6, the liquid refrigerant is placed in heat exchange relation with air from compartment 12, the air being cooled and the liquid refrigerant being evaporated. As stated above, the evaporated refrigerant returns to compressor 2 through suction line 10.

At start-up, pump 21 forwards oil to the moving parts of the compressor and to power elements 22 through lines 23. Application of oil pressure to power element 22 raises piston 49, pivoting lever 51 to move pins 37 downward, thus placing suction valve 35 in position to close port 42. It will be appreciated oil line 25 connects lines 23 with the sump of the compressor. Valve 27 placed therein ordinarily is in a closed position during operation of the refrigeration system. Valve 27 is responsive to pressure in liquid line 7 since it is connected thereto by line 32. When solenoid valve 14 is in an open position permitting condenser pressure to exist within line 32, such condenser pressure is applied against one side of diaphragm 290i valve 27 forcing the valve member 30 of said valve to close port 31 therethrough thus preventing oil flowing through valve 27 to the sump of the compressor.

It will be appreciated that opening of valve 27 permits oil in lines 23 to flow to the sump of the compressor, thus preventing the application of a predetermined oil pressure against power elements 22.

When temperature in storage compartment 12 drops to a predetermined point, such temperature being indicated by bulb 16, thermostat 15 opens an electrical circuit to de-energize the solenoid of valve 14 to move the valve to a closed position, preventing passage of liquid refrigerant from receiver 5 to evaporator 6. Since compressor 2 continues in operation, it will be appreciated the pressure then existing in liquid line 7 between valve 14 and expansion valve 8 corresponds to evaporator pres- A piston spring 54 sure rather than condenser pressure. This reduction in pressure applied against diaphragm 29 permits spring 33 to move valve member 30 away from port 31 permitting oil to flow from line 25 to the sump of the C0111- pressor, thus preventing the application of effective oil pressure applied against power elements 22. Since the oil pressure applied against power elements 22 is not sufiicient to hold pins 37 in downward position, piston 49 of power element 22 drops, thereby pivoting lever 51 in the opposite direction raising pins 37 to move valve 35 away from port 42 unloading the compressor cylinder thereby achieving automatic unloading and automatic evaporator pump down with a continuously running compressor when refrigeration is not desired.

It will be appreciated compressor 2 is driven by a prime mover (not shown) such as a direct drive internal combustion engine. This is particularly desirable when the refrigeration system is used to cool the storage compartment' of a vehicle such as a truck or trailer. In such circumstances, the'cornpre ssor may be operated continuously and may be automatically unloaded when refrigeration is not required, thus preventing the temperature of the storage compartment from falling to an undesirable point. r

Valve 27 may be set to operate at any desired pressure. Preferably,it is set to operate at a pressure above atmospheric pressure and below the minimum anticipated condensing pressure. It has been found that a setting of 10 to 25 p. s. i. g. is satisfactory.

The present invention provides a simple, ready capacity control for the reciprocating compressor of a refrigeration system. The unloading mechanism and power elements are inexpensive, while operation of the unloading mechanism is controlled by an inexpensive valve, which may be an automatic expansion valve with an external equalizer, if desired. The present invention is particularly adapted to use in transportation under circumstances requiring continuous operation of the compressor.

The use of unloading mechanism on each cylinder of the compressor reduces the starting torque of the compressor to an absolute minimum. I This is of great advantage when the compressor is driven by an internal combustionengine since it is relatively simple and easy to start: the engine without a clutch.

While I have described a preferred embodiment of the present invention, it will be understood the present invention is not limited thereto since it may be otherwise embodied within the scope of the following claims. I claim: I 1. In a refrigeration system, the combination of compressor, a condenser connected to the compressor,

an evaporator placed in a compartment to be cooled, a liquid line connecting the condenser and the evaporator, a suction line connecting the evaporator and the compressor, expansion means in said liquid line, a valve memher in said liquid line placed between the condenser and the expansion means for controlling passage of refrigerant from the condenser to the evaporator, means for rendering a suction valve of the compressor inoperative while continuing operation of the. compressor, said means being responsive to pressure in said liquid line,

and a control for said valve member actuated in response to a predetermined change in temperature in the compartment being cooled.

2. In a refrigeration system the combination of a compressor, a condenser connected to the compressor, a liquid line connecting the condenser with an evaporator placed in a compartment to be cooled, a suction line connecting the. evaporator and the compressor, expansion means in said liquid line for regulating how of refrigerant to the. evaporator, unloading mechanism to. unload the compressor, said unloading mechanism being actuated by oil pressure, a valve member in the liquid line between thecondenser and the expansion means, said valve memher being open under normal operating conditions when it is desired to utilize the compressor to provide refrigeration, closing of said valve changing pressure in the liquid line from substantially condenser pressure to substantially evaporator pressure, and a valve member directly responsive to change in pressure in the liquid line for changing the oil pressure imposed on the unloading mechanism.

3. In a refrigeration system the combination of a compressor, a condenser connected to the compressor, a liquid line connecting the condenser with an evaporator placed in a compartment to be cooled, a suction line connecting the evaporator and the compressor, expansions means in said liquid line for regulating flow of refrigerant to the evaporator, unloading mechanism to unload the compressor, said unloading mechanism being actuated by oil pressure, a valve member responsive to change in pressure in the liquid line for changing the oil pressure imposed on the unloading mechanism, a second valve member placed in the liquid line between the con denser and the expansion means for controlling passage of refrigerant from the condenser to the evaporator, and a control member for said valve actuated in response to a predetermined change in temperature in the compartment being cooled.

4. In a refrigeration system, in combination with a compressor including compressing elements, a crankcase and unloading elements for each cylinder, a condenser connected to the compressor, an evaporator placed in a compartment to be cooled, a liquid line connecting the condenser and the evaporator, a suction line connecting the evaporator and the compressor, expansion means in said liquid line, power elements for unloading the cylinders of the compressor, oil lines connecting the power elements with the crank-case of the compressor to permit oil pressure to be applied to the power elements, a valve in said liquid line between the condenser and the expansion means to regulate flow of refrigerant from the condenser to the evaporator, 21 control for said valve actuated in response to predetermined change in temperature in the compartment being cooled, and means responsive to pressure in the liquid line for regulating oil pressure applied to the power elements.

5. A refrigeration system according to claim 4 in which an oil pump is provided to supply oil to the power elements and an orifice is provided in the discharge oil line to regulate oil pressure, said means responsive to pressure in the liquid line for regulating the oil pressure imposed on said power elements being a valveincluding a diaphragm flexed by pressure in the liquid line.

6. In a capacity control arrangement for a reciprocating compressor employed in a refrigeration system, the combination or" power elements to unload the cylinders of the compressor, said power elements being actuated by oil pressure, a first valve responsive to a change in pressure in the liquid line of the refrigeration system to vary oil pressure imposed on said power elements, a second valve in said liquid line between the condenser and the expansion means of the refrigeration system and a control adapted to actuate said second valve in response to a predetermined change in tempcrature in a compartment being cooled.

7. In a refrigeration system the combination of a compressor, a condenser connected to the compressor, an evaporator placed in a compartment to be cooled, a liquid line connecting the condenser and the evaporator, a Suction line connecting the evaporator and the compressor, expansion means in said liquid line, a solenoid valve in said liquid line placed between the condenser and the expansion means for controlling passage of refrigerant from the condenser to the evaporator, means for rendering a suction valve of the compressor inoperative while continuing operation of the compressor, said means being responsive to pressure in said liquid line and a switch through which current is supplied to energize the solenoid valve, said switch being actuated in response to a predetermined change in temperature in the compartment being cooled.

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